Method of and apparatus for measuring fluids



Jan. 19,1932.

M. E; BENE-:SH v METHOD OF AND APPARATUS FOR MEASURING FLUIDS Filed Jan. 26

als

and pressure variations of the fluid being measured.

A still further object ofthe entire inven-v tion is to provide a fluid meter which is independent of the eiect of specific gravity of the uid. y

Still other and ancillary objects and advantages of the type of meter herein disclosed willbe apparent from the ensuing description.

Primarily the invention in its broadest aspeet utilizes a primary element having a 'nown relation between the fluid flow and a ressure head produced by the flow, comined with apparatus which is operated to produce an equal, or effectively equal, and o posite pressure, there being a known relation between the pressure produced by said apparatus and some measurable factor concerned in its operation.

In all of these meters the rate of How is customarily taken as proportional to the square root of the differential ressure. Prior to this invention the dierential pressure was measured in terms of some other uid than that being measured, and this of necessity introduced many difficulties since the relative densities of the measured and the measuring fluids had to be known. Also, as stated above, a mechanism for taking square roots of this differential is necessary before a rate of ilow is determined and a further mechanism is re uired to integrate this rate and obtain a tota ow.

In the present embodiment of this invention, the diderential pressure developed by the action of a iuid on the primary element of any head type meter, is balanced b the pressure developed across the inlet an outlet of a centrifugal an, making use of the same Huid under the conditions obtaining in the primary element. Itis well knownthat under the condition of zero or small Bow the pressure developed by a centrifugal fan is practically proportional to the square of the fan speed. This is equivalent to saying that the fall s ed is proportional to the square root of e fan, that is, the rpressure between the inlet and the outlet. he rate of iow in a head type meter is also proportional to the square root o the diierential pressure produced by the action of the uid on the primary element. Therefore, when these two pressure dierences are balanced or equal, the fan speed is directly proportional to the rate of How, and consequently the totall number of revolutions is proportional to the total ow. Thus, b this invention, the rate of flow can be in icated, being proportional in /ltlie rlixresent embodiment to the rotative speed of. t e fan, and the integration is accomlished by a mere revolution counter, which 1s indicating and registering.

When theuid dow is required in terms pressure developed by the of conditions different from those existing in the fiuid a correction may be required for temperature pressure and in the case of gas also saturation. This correction is automatically made by varying the speed ratio of the fan to revolution counter in accordance with the combined effect of these factors.

In the accompaning drawings I illustrate more or less da rammatically a combination of structures w ich cooperate to produce a meter of the type described, the parts being correspondingly numbered in the several figures. The device illustrated in the drawings represents a completely operative meter in which the essential features of the invention are exem liied for the purpose of explanation of t e character of the invention.

In the drawings, Figure 1 shows a fluid meter especially adapted for measuring gas flow in accordance with the present invention.

Fig. 2 is a detail view of a compensating device associated with the fan.

In the drawings, the numeral 5 represents a gas main in which the flow in the direction shown by the arrows in Fig. 1 is to be determined. In the main 5 there is a suitable rimary element here reipresented by the orice 6. Ihe action of the uid iiowin through the orifice 6 creates a di'erence ol 'pressure on the two sides of the primary element. Pipes 7 and 8 lead to the two sides of the primary element, the the pipe 8 being own-stream with relation to the orifice 6. The pipes 7 and 8 lead to a pressure creating means which is of such a .character that it is arranged to produce in each ipe a pressure equal to the up-stream and doWn-stream pressures at the points 9 and 10, these being the points of entrylrespectively of the pipes 7 and 8. In the present meter the pipes form a closed circuit through a ian 11 enclosed in a fan casing 12, ipe 8 leading to the fan inlet and pipe 7 eading to the fan outlet.

The fan casin 12 and the pipes 7 and 8 are maintained at t e same temperatures as the iuid in the main 5 at the rimary element 6. This is referably accompllshed by providing a close housing 13 for the fan casing throu h which Huid from the main is circulated. n inlet pipe 14 leads from the main 5 into the housing 13. lipes 7 8 and 14 and the housing 13 are suitably insulated as indicated enerally at 15. An outlet pipe 16 romthe ousing A13 is connected to a suitable circulatin means which draws iuid through the housing from the main 5 and Vreturns it throng pipe 17 to the main.

Impelling meansis also required to operate the fan system. The circulating means above mentioned may be of any suitable character but I prefer to combine it with the means which produces operation of the fan 11 enclosed in the fan casing 12. A fan shaft 19 is provided 'extending through the casing ipe 7 being up-stream and 12 and the housing 13 into a second fan casing Y wherein is located an impeller fan 21 servthe fan 11 in accordance with the degreepfV opening of the valve 24. In the present stance a portion of the gas.l which flows through the housing 13 is recirculated to drive the impeller fan 21, since the pipes 16 .and 17 are yconnected. so that the blower 27 circulates gas through the housing 1-3. This is accomplished by tapping pipe 17 into pipe 22 and `by connecting pipe 16 to pipe 25. Any suitable driving means as the motor 28 is provided to, operate the tan 27. Y

The fan 1l is, in the present instance, of a centrifugal type with blades 29 thereon be- V sired forni, herein 40 Vtion between the drum 32 and the tween disks and 31. .on its outside a drum ory boX'32 into which The disk 3() carries gas from pipe 8 is adapted to dow axially.

i The box has a tubular bearing 33 journa'led in the fitting 34 in the fan casing and made gas tight with reference to the fan chamber, of the casing 12. The pipe 8 is connected into the fitting A34.. A, stud or finger 35l rigidly mounted `within the fitting 34 carries radially arranged stationary blades 36 resembling a fan in the drum 32, so that as the drum revolves the fluid therein will be held relatively stationary. A slot 37 (Fig42) is provided in the fan disk 30which slot may be of an)7 debeingshown radially lo`- cated a short-distance from the axial center ofthe fan. The 4slot 37 aords'communicay space between the blades of the fan.

With the gas in the fan casing 12 under tliesame conditions of temperature, pressure and saturation as in the main pipe, it follows that when the pressure diii'erential across the orifice 6 is balanced b 'the fan 11, the

rate of ilow (in units of vo` urne under eXist- Y ing conditions per unit time) through 'the orifice 6 is directionally proportional to the fanspeed (revolutions per same unit of time) and the total fiow in a given time isproportional to the total number of fan revolutions in the same time. The above assumes that the laws of the fan and of the primary element of the head meter `(here orifice 6) are similar. To illustrate, the rate of flow through the orifice is proportional to the square root of the differential pressure developed across openings 9 and 1G, and the fan speed is also proportional to the square root of the same differential pressure since a balance obtains.

Such perfect similarity between the law of the primary element and the law of the sec,- ,ondary element is not essential to this invention providedonly that both of these laws are known. This is true because of the provision of a compensating device which autom matically adjusts for a diference of these laws. Thus, in the present embodiment, the

relation between the pressure differential developed by the tan and its speed'need not be exactly the same as the relation between the flow and the diderential pressure developed by the action of that ilow on the primary element.

in the present instance, such a compensation device is provided. This is in the nature of an additional member, the design of which may vary for different meters. It is of such a character that it provides a slot crossing slot 37 at different positions along the slot 37 and so varying the position of the inlet from the center ofthe fan. In the present instance the position of this slot intersection which forms the effective inlet to the fan depends upon the fan speed. The structure by which this is obtained' is as follows: There is provided a disk or plate 38 rotatable with respect to the fan body, The plate 38 is rotatably mounted on disk 30 by a pin 39 rigid with the plate 38. A pinion40 is also rigid with the plate 38 for actuation by va speed governor which rotates the plate relatively to the fan as the fanspeed changes. The governor may be of any desired type. Herein I show interlocked racks 41 and 42 eachin mesh with opposite sides of the pinion 40. Each rack passes through an enlarged ri ht angular projection 43 of the other rack, t us forming a rectangular structure expansible in the direction along the racks. side of the racks tends to compress the redtangle. Guide extensions 45 at the ends of Springs 44 alongthe racks pass through guide blocks v46 mounted on -the :tan disk 30. These guide extensions and the meshing relation of the racks with the pinion are the sole support for the speed governor. As the fan rotates at a given speed the plate l38 is carried with it,

the rack projections 43 being separated'` aga-inst the springs 44 a distance dependent on the speed of the fan. As the speed changes, 'the relative -motion of the racks causes the pinion 40 to turn the plate to -a new position. Hence, for each speed of the fan, plate 38 and disk 30 occupy agiven rela tive position. A slot 47 is provided in the plate 38. Since this plate 38 is rotated by the above described mechanism', the slot 47 crosses slot 37 transversely at any ldesired posit-ion according to the speed of the fan. The proper position and shape of 'slot 47 in any meter ot this character is determined by calibration. Herein slot 47 is shown spiral but it is understood 'that this is arbitrary and merely exemplary for this instance.

Of courseit is vdesirable to keep the pres-` sures of .the primary element and of the fan continuously balanced against each other.- However, when a variation in How through the main 5 takes place, there will be a corresponding pressure change at the points 9 and 10. Il the fan continues to move under these new conditions at its Aformer speed the pressure will be unbalanced and a flow will' take place through the fan system. The relative pressures will be only slightly different so that the fan iiow will be small. For high precision it is necessary to have very delicate and responsive fan speed governing means which will detect this flow and operate to stop it thereby reproducing the balanced condition. Various mechanical, electrical or other devices may be inserted in the fan system for this purpose.

In the present instance I have provided a thermal fan speed governor which provides high sensitivity. This sensitivity is possible because the inertia of the governor, which a difference in balance in pressure must overcome, is merely the inertia in the governor, the fan and the connections. Such a governor is of great advantage in the null method of balancing pressures here used. Thus, the primary element need not develop a high differential for the meter to give a high order ot precision over a very wide range of flow rates. In the insulated 11p-stream pipe 7 I place a heating element which may be of any character. I prefer an electrically heated grid 48 held at a reasonably constant temperature by a rheostat 49 in series with van electrical energy source 50. In close proximity to the grid 48 and in line with the flow past the grid, I fix to the pipe 7 one end of a thermal expansion element herein illustrated as an expansive rod 51, which passes through the pipe to the outside. The rod 5l is ixed to pipe 7 by a suitable connection 51a. In a balanced condition of the fan and primary element differential pressures, the element 5l has been raised in temperature to some extent by heat from the grid. By flow of gas from the main into the pipe 7, the gas heated by the rid heats the thermal element to expand it. y a reversal of flow from the pipe 7 into the main the cooler gas in the" system (maintained cooler by the lower temperature 'of housing 13) Hows past the thermal element 5l and cools it. Thus, the free end 52 of the thermal element is raised and lowered according to the direction of flow in the fan system. I utilize this motion, which is capable of exerting considerable force, to control the valve 24 in a direction dependent upon the length of the thermal element, any suitable means being interposed between the thermal. element 51 and the valve 24. In the present instance, I provide a continuously revolving disk 53 turned by suitable gearing 54 con-v nected to the motor 28. The valve stem 55 of valve 24 is extended at 56 to carry a fricwhich carries tion disk 57 which is suitably arranged to enf ga e the disk 53 for turning the valve 24. l

n the balanced condition of the metertli point of contact of disk at the center of the disk 53 so that no motion of the valve will result. However, if there is a flow throufrh the up-stream pipe 7 into the main 5 it indicates that the fan is revolving faster than is necessary for a balanced condition. Under this condition the thermal element will be cooled by the flow, and to reach a balanced condition, it is necessary that valve 24 be closed to some extent. This. is effected by maintaininv the disk 57 slidable on the extension 56 an by engaging it in the hifurcatcd end ot a lever 58 pivoted at 59. The thermal element 5l is secured to the lever 58 by a screw adjustment 60 so that the relative position of the end of the element 51 and the lever 58 may be varied. By suitably roportioning these parts to the characters o the valve 24 and of the blower fan 27, the fan 11 will be automatically maintained at the speed necessary lfor the fan to balance the pressure differentil developed by the action of the uid on the primary element.

From the foregoing, it will be clear that the number of revolutions made by the fan 11 in a given time will be directly proportional to the total ilow through main 5 in the same time, just as in ameter of the positive class, and the number of revolutions will be in terms of units of volume of the fluid under the conditions in the main. When it is desired to express this Volume in terms of some standard conditions of temperature and pressure, and in the ease of gas, saturation, or when it is desred to use some other units than volume, such as mass, it is necessary to apply a correction. In this meter the correctionis applied automatically by varying the speed ratio between the fan l1 and a register in the form of revolution counter 61. The ratio is provided by suitable gearings 62 and 63 from the tan shaft 19, gear 63 being used to drive the register. The speed ratio between the register 61 and the gear 63 is variable by any suitable means. In the present instance this consists of a. friction wheel 64 operating the register which engages on the face of gear 63 at varying distances from the center. An expansible diaphragm or bellows is fixed at one end in a closed chamber 66 located within the housing 18. The bellows is filled with a fluid following the same law as the fluid bein measured and is then sealed. A pipe 67 adords communication'from the chamber 66 to either one of the pipes 7 or 8, in the present instance the nearest pipe 7 being chosen. the temperature and pressure in the chamber 66 vary, the bellows 65 operates a plunger 68 the register 61 and friction wheel 64. Since the temperature of the housing 13 is maintained the same as the main, and since the pressure in chamber 66 is that 57 on disk 53 is lmade 4Lacasse' f the Igas in main 5 is saturated with water vapor and it is desired to correct for this, a small quantity of water 69 is placed inside the bellows 65.

lit is apparent that the adjustment of the `differential pressure developed by the secondaryelement so as to balance the diiferentia-l pressure developed by the action of the fluid on the primary element, requires an appreciable time with the described or any other type of fan speed Igovernor. Other types of vgovernors such as purely mechanical t pes (not thermal) may easily be made to ave less, but not zero, time lag, but at a sacrifice of sensitivity. As beforeexplained, the action of the thermal fan speed governor here described should be such that it adjusts the speed of the fan 11 so that the total gas flowing over expansion element 51 in one direction is equal to the total flow in the opposite direction. Since in normal use neither the flow in main 5 nor the speed of power motor 28 are constant, and since there are lags in the adjustment ofthe speed of fan 11 to balance the flow of differential, it is important for the most accurate workingr of the meter thatY the flow inthe main 5 corresponding to these small temporary dierences between the tan and true flow differentials be integrated by the fan with the desired precision. Theretore, l provide a flow control means, which, in conjunction withv the fan speed governor, assures the desired precision in integration by the tan of these small temporary dierences between the fan and true flow differentials of the primary element.

The'total quantity of gas flowing in either direction over the expansion element 51 is controlled by a so-called fan flow control which is preferably constructed as a constricted Vpassage 70 in the fan connection 7. This particular one -is so designed that its dow coemcient is the same for both directions ot dow and so that it oerspractically the total resistance to dow through the fan speed governor, the tan 11 and its connection pipes 'Y and 8. That the dow coeflicient of the ten ilow control be ythe same in both direcv tions is preferred but this is not indispensable.- lt desired, the flow coefficient of the flow control I in one direction of now may be made different from that in the opposite direction throngh'the flow control so as to automatically'compensate for variationsof ,gi-ear 53, valve 24 being closed.

the law of the fan due to a tlow occurring through it. If the flow coeilicient of the flow control is not the same in both directions of dow-through it, periodically reversing the connections to the fan tlow control amounts to having the coellicient the samein both directions. When necessary mechanism for periodically reversing the connections may e provided. It is preferable that such periodic reversing means be timed with respect to thnarotations'of the tan shaft 19, whereby tlilefperiods of reversal will be controlled not by time but in accordance with How in main 5. Any suitable means may be employed 'for this purpose. In the present instance wherer small variations in the new diterential ranaprovided for and where a clean gas is handled, this is not required.

Although the fan flow control is here shown as a constricted portion ot the pipe 8, it will be understood that its design will in general depend upon the primary element with which it is to be used, the ow conditions, and the metering precision desirel. In general, `the flow through the fan fiow control 20V will he proportional to some other power of dierential head causin the How the difference between the fan ancgl primary element differentials) than the power of the ydiitl'erential head to which the flow in the primary element is proportional. 4For example, as in the present instance, where the how through the orifice 6 is here considered proportional to the one-half power of the differential developed across it then for ordinary precision, the iiow through the fan llow control 70 may be considered proportional to the first power of the differential pressure acting across it, i. e., to the diner- .ence between the di'erentials of fan 11 and orice 6. lt is to be understood 'that the llow control means maybe varied in structure and operation in accordance with the above suggestions as required bythe parts with which it is associated.

ln the above described meter with no flow in main 5, the following conditions obtain. Zero How through the main gives zero di'erential pressure between points 9 and 10. This means that the diderential developed by the fan 11 is also zero and that the fan is stationary.V Grid 48 is at its reasonably constant temperature and the rod 51 holds the friction wheel 57 in the neutral position on The motor 28 is continuously operating whereby the temperature of housing. 13 ,is maintained at the same temperature as the duid in the main 5.

As soon as a dow starts through main 5 and the orifice 6, a tlow ot gas also starts into pipe 7. This gas being heated in passing over grid 48, raises the temperature of the rod 51 and so causes valve 24 to be opened, which results in rotation of the fan 11, tending to balance the differential pressureacross orifice 6.

When the differential pressure develofped byfan 11 exceeds that developed by the ow through orifice 6, the reverse takes place, that is, the gas from the fan Hows over and lowers the temperature of the expansion rod 51 thereby gradually bclosing the valve 24 and reducing the speed of the fan 11.

Under the ideal condition of a constant rate of flow through the orifice 6 and with a perfectly constant speed of motor 28, the tan speed will be constant, the an s eed governor will be in neutral osition, an the registration at counter 61 will at alltimes be precisely proportional to the total flow through orifice 6, even though the temperature, pressure and specific gravity of the gas should vary.

Normall such conditions do not obtain in ractice. either the flow through the orice nor the motorspeed will be constant. To

illustrate the action of these variations it may be assumed that the s eed of the motor 28 is constant and that t e flow varies as now to be explained. It is understood that this variation is relative and that the eX-v ample will apply when either or both flow and motor speed variations occur.

Starting with a perfect balance between 'the fan and the flow diserensns (that is,

friction wheel 57 at neutral position), let the flow in main 5 be increased to a new constant value. The resulting iiow of gas over grid 48 will expand rod 51, displace the wheel 57 from neutral position in a direction to cause valve 24 to be further opened and so increase the speed of the fan 11. The speed of fan 11,will continue to be increased so long as the position of wheel 57 is on the opening side of neutral position. Thus, when the fan differential exactly balances the new constant value of the flow differential,`

the friction wheel is still on the opening side of neutral position and continues to cause increase in speed of the fan 11. Thus, the fan differential exceeds the flow differential and a reverse of the vpreceding operation takes place-,that is, the iiow from fan 11 over rod 51 cools the rod 51 and returns wheel 53 to neutral poistion. It would appear from this that the system will continue to so hunt under constant flow and constant speedf conditions. However, the construction of the fan speed governor is such that there is a slight but adequate heat loss from the rod 51 at all times. In the present instance, this may take place at the support 51 of the rod 5l to pipe This serves as a damping means so that successive oscillations under these ideal conditions grow less.

At each instant when the disk 53 is at its neutral position the registration of counter 61 gives precisely the true total flow through main 5 up to'that instant. This is happenis for all practicall purposes entirely negl ligible.

In the above description of the illustrated embodiment of the invention, it is to be understood. that various parts may be replaced by equivalent devices of varying nature. For example, the fan impeller 21 and the control valve 24 therefor may be replaced by an electrical driving and control means. The fan speed governor, including the grid 48 and the thermal element 51 with the operatin mechanism to valve 24, may be replaced y any other flow detecting and governing means. The fan fiow control may be of another character and may be incorporated into the fan speed governor in the fan system to serve as the fan flow control, flow detector and fan speed governing means.

It will thus be seen that I have provided a type of meter which is suitable for the measurement oi fluid whether it be gas, vapor or liquid or a mixture of these. It is an important feature of meters embodying this invention that in measuring fluids they will register the rate of flow or total flow in terms of an desired units, that is, the registration is in ependent of changes in density of the fluid. Furthermore, in the case of a saturated gas the registration may be corrected for saturation tothe desired basis and is independent of changes in specific gravity, temperature and pressure.

To one skilled in the art it may readily occur from the above that many other applications of the Ioroad principle of balanclng pressures are possible by using certain of the elements of this invention.

The above described and illustrated embodiment of the invention is not to be construed as a limitation of the invention and many other embodiments thereof are contemplated herein as will be clear from the expression of the invention in the appended claims.

I claim as my invention:

1. A flow meter comprising, in combination, a primary element adapted to produce a dierential pressure in known relation to the flow acting on said element, an encased fan adapted to produce a pressure in known relation to the speed of the fan, means to drive the fan, communicatlng means for Huid between the fan and the low element whereby the pressures of each may oppose each other,

Lacasse fan speed controlling means, associated with said communicating means, said speed controlling means being responsive to the flow ofluid through said communicating means, whereby a tluid flow through said communieating means operates to ail'ect the t'an driving means to change the speed of the tan thereby tending to balance the opposed pressures, the speed of the lan being indicative of the rate ot flow in the balanced condition of the pressures.

.2. A How meter comprising, in combination, a primary element adapted to produce a dilerential pressure in known relation to the flow acting on said element, an encased fan adapted to produce a dilerential pressure in known relation to the speed vof the ian, means to drive the fan, communicating means -betwecnthe fan and the primary element whereby the pressures of each may oppose each other, a heating means in said communieating means, a thermal expansion element in line with and nearsaid heating means, said thermal clement being arranged for expansion and contraction as its temperature is changed by a flow of fluid to or away from the heating means past said thermal element, and means operated by said thermal element to vary the speed ot thev fan to ettect a balancing ot pressure. in said communieating means to prevent a llow therein, whereby the speed of the fan indicates the flow acting on the primary element.

3. How meter comprising, in combinat1on. a primary element adapted to produce a differential pressure in known relation to the flow acting on said element, an encased fan adapted to produce a pressure in known relation to the speed of the tan. a fluid operated motor to turn the fan. a valve to control the duid 'tor said motor, communicating means between the fan and the primary elcment whereby the pressure of one may oppose the pressure of the other, a heating member in said communicating means, a thermal expansion element in line with and near said heating member` said element being arranged for expansion and contraction as its temperature is changed by a tlow ot fluid-to or away from the heating member past said thermal element` a rotating disk, a 'friction wheel engaging said disk, means operatively connecting said friction wheel to said valve and effective upon rotation of said wheel to adjust said valve,means connected to said thermal element and to said riction wheel to bold the latter in posit-ion i -to engage the rotating disk at the center thereof in the balanced condition ot the two pressures, said connecting means being moved by a variation in the length ot the thermal element to move the friction wheel in contact with said rotating disk on either ot the op posite sides of the center whereby to vary the tluid dowing through said valve to said motor to change the speed of the tan to a pressure- Y balancing speed.

4. A tiow meter Vcomprising, in combina-l tion, a primary element adapted to produce a differential pressure in knownrelation to the flow acting on said element, an encased fan adapted to produce a differential pressure in known relation 'to the speed ot the tan,

means to drive the tan, communicating means between the fan and the primary element whereby the pressure of each may oppose the pressure of the other, a heating member in said communicating means, a thermal expansion element in line with and near said heating member, said thermal element being arranged for expansion and contraction as its temperature is changed by a dow of luid to or away from the heating means past said thermal element, a power operated control to vary the speed of the fan, said control comprising a driving element, a power driven element adapted to have a neutral, forward or backward connection with said driving eletion to the speed of the "fan, means arranged lto oppose the pressure of the primary element against the pressure of the fan whereby when said pressures are unequall a now takes place through said-means and through the encased fan, and a fan flow7 control havling a control element arranged in said means and responsive to the flow through said means. said `flow control being operable to limit the flows through said fan so that these flows have a predetermined relation tothe ditlerences in the opposing pressures producing them.

6. A tluid meter comprising, in combination, a primary element adapted to produce a differential pressure in known relation to the flow acting on said element, an encasedV fan adapted to produce a pressure in known relation tothe speed ot the fan, communieating means arranged to oppose the pressures ot the primary element and of the tan, whereby when said pressures are unequal a dow takes place through said means and through the encased tan, said communicating means having a constricted opening therein adapted to resist a flow of fluid therethrough in an unbalanced conditional` the pressures, and being further adapted to permit-unrellt) sisted communication therethrough when the pressures are balanced.

7. A fluid meter comprising, in combination, a main for fluid, a 'primary element in said main adapted to produce a differential pressure in known relation to the flow acting on said element, an `encased fan adapted to produce a pressure in known relation to the speed of the fan, means permitting opposition of said pressures, a housing surrounding ,said encased fan, means arranged to circulate fluid from the main through said housing whereby to keep the temperature of the fan casing the same as the temperature Yof the fluid in the main, and means adapted to drive the fanl through the action of the cir culating fluid.

8. A fluid meter comprising, in combination, a main for fluid, a primary element in said main adapted to produce a differential pressure in known relation to the flow acting on said element, an encased fan adapted to produce a pressure in known relation to the speed of the fan, means permitting opposition of said pressures, a housing surrounding said encased fan, and means arranged to circulate fluid from the main through said housing whereby to keep the temperature of the fan casing the sameas the temperature of the fluid in the main.

9. A kfluid meter comprising, in combination, a primary element adapted to produce a differential pressure in known relationto the flow acting on said element, an encased fan adapted to produce a pressure in known relation to the speed of the fan, means permitting opposition of said pressures, a housin'g for said encased fan, circulating means arranged to circulate fluid from the main through said housing whereby to keep the temperature of the fan casing the saine as the fluid in the main, a closed circuit included in said circulating means, a fan in said closed circuit, avalve in said circuit, means in said `the fan, connecting means for first mentione means responsive to variations" in flow due to a difference in said pressures, means connecting said last mentioned means to said valve to adjust said valve so as to control the speed of said last mentioned fan, and means in said circulating means tov drive said first mentioned fan toa speed proportional to theiopeing ofsaid valve so that said pressures will be balanced.

t 10. A fluid meter comprising, in combination, a primary element adapted to produce a differential pressure in known relation to the flow, an encased fan adapted to produce a pressure in known relation to the speed of bringing said pressures into opposition, means providing an inlet to thefan, and means including a part adj'ust'ably coacting with said inlet to define an effective opening therethrough, said last mentioned means being carried by the fan for adjusting the location of the effective ythe fjan may be made `ment.

11. A fluid meter comprising, in combination, a primary element adapted to produce a differential pressure in known relation to the flow, an encased fan adapted to produce a pressure in known relation to the speed of the fan, connecting means for bringing said pressures into o position, means providing an inlet to the an, a'certrifugal governor device on said fan movable to a predetermined position according to the speed of the fan, and means coacting with said inlet to define an effective opening therethrough, and bein operable by said governor to adjust the e ifective opening through the inlet radially of the fan to a position determined by the speed of the fan.

12. A fluid meter comprising, in coinbination, a primary element adapted to produce a differential pressure in known relation to the flow, an encased fan adapted to produce a. pressure in known relation to the speed of the fan, means to balance the pressures, a re 'ster to integrate the revolutions of the fan directly in flow units, and variable speed gearing between said fan and said register, and means subject to the temperature and pressure of the fluid flowing through said' fan for adjusting said gearing to compensate for changes 1n the proportionality factor between the flow units and revolutions.

13. ln a gas flow meter having a member revolvin at a speed proportional to the rate of flow t rough a gas main, a register o erated by said member, a variable ratio riction gearing between. the register and the revolving member, a single expanding means affected by changes in temperature and pressure in the main, and operating means associated with the expanding means and the friction gearing to vary the driving ratio between the member and the register.

14. In a gas flowl meter `having a member revolving at a speed proportional to the rate of flow through a gas main, a register operated by said member, a variable ratio friction gearing between the register and the revolving member, a sealed bellows containing gas maintained under the same temperature and pressure as the gas in the main, andmeans connecting said bellows with said friction gearing whereby to alter the driving ratio etween the register and the revolving mem- 15. In a fluid meter of the class described having two opposing differential fluid pressures, a communicating system for said opposing pressures wherein a flow of fluid takes place when said opposing pressures are unbalanced, means responsive to a flow in said releases system, means actuated by said responsive means to cause said opposing balanced, a device through said communicating system, said device permitting unrestricted static pressure communication, whereby the desired precision in metering is obtained and damping means in said system opera le to decrease successive flows through said system to approach a balanced condition of the pressures.

' 1G. A fluid meter of the class described comprising, in combination, a lsource o differential pressure, an encasedv fan, connections from the inlet and outlet of said fan to said source or dilierential pressure, means to operate the fan, control means to regulate the speed of the Jian to balance the diierential pressure of the ian against the differential pressure of said source, said last mentioned means including actuating means in the conn nections responsive to a tlow through the connections caused by unbalanced pressures, the actuation being ei'ected in such a manner that a iiow in one direction slows the ian and a flow in the other direction speeds up the fan, and a device or retarding the ilow through said connections, said device permitting unrestricted staticv pressure communication, whereby the desired precision in metering is obtained.

i 17. A. fluid meter of the class described comprising, in combination, a source ci diterential pressure, an encased ian, connections rom the inlet and outlet of said fan to said source of diierential pressure, means to operate the ian, control means to regulate the speed of the fan to balance the diterential pressure oi the fan against the differential pressure of said source, said last mentioned means including actuating means in the connections responsive to a tiow through the connections cause by unbalanced pressures, the actuation being enected in Such a manner that iiow in one direction slows the ian and a iiow in the other direction speeds up the i'an, and a portieri in one of said connections forme into restricted passage having known coeiiicients of fioW in cients of iiow being chosen to eiiect the desired precision in metering even though there are temporary di'erences between opposing pressures.

18. A fluid meter having, Y

primary element wherein the diderential ressure is approximately proportional to the square of the duid ow, a ian arranged to produce a diierential pressure approximate- 1y proportional to the square oi the speed of the ian, connecting means permitting'the opposition oi said differential pressures, a an flow control in said means in lthe form oi a constricted tubular passage having a dow c0= efficient in both directions which varies approximately as the first power oi the dierpressures to be in combination,

entiai pressure acting on said passage, whereo for reta ding the ioW byto edect the desired precision in even though there are temporary dierences between the fan and true iiow dierential pressures, a drive for said ian, means responsive to the flows caused by said diterences, and a ian Aspeed governor operable by said means to ei'ect changesy in the fan speed in a direction to vary th metering,

e fan iiow. 19. A fluid meter having a primary element wherein the action of the iiuid fiow produces a ldifferential pressure in said element, means housing a bo y of said tohold said tionsof temperature as prevail at the primary element, means acting upon said body o uid in such a manner as to produce a diderential pressure therein, the differential pressure o said 'means having a known relation to its operation, means permittin opposition of said dibrential pressures, w ereby the operation of said means in balancing said ifi ential pressures becomes a measure of the fiuid iiow acting upon the primary element.

In testimony whereof, i have hereunto aifixed my signature.

MATTHEW E. BENESH.

both directionstsaid coeihl Y iiuid, meansv body of iuid at the same condi. 

